Highlights from X-Ray Grating Spectroscopy

1. HighlightsfromX-Ray Grating Spectroscopy Cambridge MA July 2007 Ehud Behar Department of Physics, Technion, ISRAEL

2. Outline • Choice of Topics • things you might not have thought you could measure - a biased view • Spectral line profiles • gas kinematics • beyond instrumental resolution • Where is the X-ray plasma? • distances from UV sources • spectral variability • Measuring column density with emission lines • in AGN • in PN • Observing thermal instabilities from inner-shell phenomena • Concluding Remarks

3. Exploiting the High Spectral Resolution • Algol: (eclipsing) stellar binary B8 V + K2 IV • “Where is the X-ray stuff ?“ • Doppler shifts accurate to ±50 km/s reveal the X-ray source: Algol B • B8 not X-ray source • Excessive Doppler widths (125 km/s) reveal beyond-thermal flows: rotation, turbulence, flare distribution? (Chung et al. 2004)

4. X-Ray Flows in  Carinae? • Massive LBV • Steady X-rays consistent with a colliding-winds binary with a 5.54 yr orbit (Corcoran et al. 2001) • Not so the intriguing ~70 dayX-ray shut down (minimum) around periastron passage, nor the preceding bright flares • Gratings: Velocity shifts and broadening during flares as system approaches periastron • Can not be accounted for by continuous wind collision and orientation effects (but see poster by M. Corcoran) Wind-wind model profiles by Henley et al. 2003

5. Spatially Resolved Spectroscopy • Giant elliptical galaxyNGC 4636 • Cross-dispersion line-ratio variation • Resonant scattering reduces Fe XVII f / r line ratio away from center • MC fit (by J. Peterson) follows photons as they scatter, constrainingvturb ≤ 30 km/s (or scattering would be quenched) • … order of magnitude better than instrumental resolution

6. Opposite Effect? • NGC 253 with RGS • forbidden line enhanced away from center • Hard to explain, but demonstrates again the performance of the gratings Bauer et al. (2007)

7. Where is the X-ray plasma?UV destruction of forbidden lines • UV flux depletes the long-lived upper levels of forbidden lines (e.g., He-like triplets) • Hence, f / i ratios sensitively probe distance from UV source • Applied to O star winds (e.g.,  Pup) - see talk by A. Pollock and poster by M. Leutenegger • Easily confused with density effect Kahn et al. 2001 r i f

8. Finding Unseen Companionswith UV Depletion Effect  Lep B

9.  Lep Astrometry  Lep  Lep B radio

10. Where is the X-Ray Absorber? Recombination/Ionization Time Scales • Reaction of absorber to increase/decrease of ionizing flux is sensitive to ionization/ recombination times • Ionization/recombination times yield distance/density (=L/nr2) of absorber from ionization source • Current grating spectrometers allow for detection of variations on t ≥ days, even for the brightest sources t ~ days t ~ months (Krongold et al. 2005)

11. Outline • Choice of Topics • things you might not have thought you could measure - a biased view • Spectral line profiles • gas kinematics • beyond instrumental resolution • Where is the X-ray plasma? • distances from UV sources • spectral variability • Measuring column density with emission lines • in AGN • in PN • Observing thermal instabilities from inner-shell phenomena • Concluding Remarks

12. NGC 1068 RGS Type-2 AGN: Discrete Emission from Photoionized Plasma

13. Line Emission Sensitive to Column Density Effect • Lines are driven by recombination (cascades) and by photoexcitation • Resonance cross sections are much higher, but … • Resonance absorption saturates => photoexcit. diminishes while recombination persists • Consequently, resonance lines dominate low NH regions (base of ionization cone) • Forbidden lines dominate high NH regions • Can intermediate line ratios mimic collisional plasma?not at high S/N • The resulting Seyfert 2 spectrum includes entire range => use average in model Absorption Emission

14. Emission Line Ratios Sensitive to Column Density

15. Not Only NGC 1068 • ~ dozens of additional sources • O VII column densities comparable to the Seyfert 1 direct-absorption measurements • Supports AGN unified scheme: X-ray narrow line region • Interesting question: What makes all the sources lie on such a tight correlation ? Guainazzi & Bianchi 2007

16. Recombination Spectra in Planetary Nebulae? 300 ks LETG observation of BD+30 PI J. Kastner, plot by R. Nordon, see talk by Young Sam Yu

17. Outline • Choice of Topics • things you might not have thought you could measure - a biased view • Spectral line profiles • gas kinematics • beyond instrumental resolution • Where is the X-ray plasma? • distances from UV sources • spectral variability • Measuring column density with emission lines • in AGN • in PN • Observing thermal instabilities from inner-shell phenomena • Concluding Remarks

18. Five Orders of Magnitude in Ionization Parameter Ability to see the full ionization range reveals exactly where thermal instability occurs

19. CONCLUDING REMARKS • Spectroscopy is where the physics is! • Grating spectroscopy has boosted X-Ray Astronomy to level with other branches of astronomy and contributed to all fields of astrophysics • The high spectral resolution has provided unprecedented plasma diagnostics • In the future we should aim at better time- and space- resolved spectra • A “highlight” talk does not provide the full picture but … • Nevertheless, some less conventional diagnostics with gratings: • Kinematics: Discerning binary and non-thermal motion, including turbulence width better than spectral resolution • UV sensitive X-ray lines: Distance from OB starsleading to the discovery of B star companions • Distinguishing between AGN and starburst line emission • Measuring column densities in emission => associating Seyfert 1 absorber with Seyfert 2 emitter • Thermal instability in AGN outflows • Of course, there are many other exciting examples

20. Many thanks to my collaborators over the years and to my students at the Technion

21. THANK YOU FOR YOUR ATTENTION

23. Cooling Curves